The present invention relates generally to apparatus and methods for cleaning thin disks, such as semiconductor wafers, compact disks, glass wafers and the like.
A conventional method for cleaning particles from semiconductor wafers is known as megasonic cleaning. During megasonic cleaning, a transducer oscillates between compressed and strained states at a near 1 MHz rate. The transducer is coupled to a fluid, either fluid in a fluid filled tank, or fluid flowing through a nozzle. The megasonic oscillation output by the transducer is thereby coupled to the fluid, causing a megasonic pressure oscillation therein. As the pressure in the fluid oscillates between positive and negative, cavitation or bubbles form in the liquid during negative pressure and collapse or shrink during positive pressure. This bubble oscillation gently cleans the surface of the wafer.
To cause the transducer to oscillate, a power supply is coupled to the transducer and is adapted to deliver energy thereto. However, due to an impedance mismatch a portion of the power supplied to the transducer typically is reflected from the transducer rather than being delivered thereto. Thus, efficiency of cleaning within the tank is reduced. Conventional megasonic cleaning apparatus provide a matching network that attempts to minimize the power reflected from a transducer, but that gleans no other information from the reflected power.
The invention provides a megasonic tank system having a controller that may monitor power signals reflected from a transducer (xe2x80x9creflected power signalsxe2x80x9d) and that may determine cleaning information based on the reflected power signals. The megasonic tank system also comprises a tank adapted to contain a fluid, a transducer coupled to the tank so as to transmit energy to the fluid, and a power supply coupled to the transducer and adapted to deliver energy thereto.
Other features and aspects of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.